The invention relates to the general field of chem. mech. polishing with particular reference to polishing surfaces of silicon oxynitride and the removal of all associated particle residue.
Referring to FIG. 1, we note that, for certain technology families notably 0.18 micron logic, it is necessary to use a layer of silicon oxynitride 13 (in conjunction with a titanium nitride layer 14) to serve as a bottom anti-reflection coating (BARC) prior to coating with photoresist. This facilitates patterning of via holes, such as 16, that will be etched through an inter-metal dielectric layer 12. The latter sits on substrate 11 which is typically a layer of wiring. This would then be followed by over-filling the via holes with tungsten layer 15. The latter is then planarized by means of CMP (chemical mechanical polishing). Planarization is performed in two steps. First, most of the tungsten is removed, as shown in FIG. 2. The wafer is then moved to a different platen where titanium nitride layer 14 and the remaining tungsten are removed, as shown in FIG. 3.
It has, however, been found that tungsten CMP doesn""t completely remove all silicon oxynitride from the surface and that a residue of silicon oxynitride particles get left behind. These are shown in FIG. 4 as particles 41 on the surface of dielectric layer 12. Several processes have been tried to cause the removal of the silicon oxynitride particles. For example, an extra step of de-ionized water (DIW)-buffing can usually achieve the removal of the particles but this is time consuming and requires another dedicated tool for the task. A process that can be added in situ to the existing process, rather than being part of a post CMP cleaning step, is also to be preferred.
A routine search of the prior art was performed with the following references of interest being found:
U.S. Pat. No. 5,704,987 (Huynh et al.) show a post CMP clean using TMAH (tetramethyl ammonium hydroxide). Naghshineh et al. in U.S. Pat. No. 6,194,366 B1 show a post CMP clean comprising TMAH. In U.S. Pat. No. 6,152,148, George et al. also show a post CMP clean that uses TMAH, as do Wang et al. in U.S. Pat. No. 6,099,662. U.S. Pat. No. 5,981,454 (Small), U.S. Pat. No. 6,044,851 (Grieger), U.S. Pat. No. 6,235,145 B1 (Li et al.), U.S. Pat. No. 6,046,112 (Wang), U.S. Pat. No. 6,114,241 (Choi et al.), and U.S. Pat. No. 5,679,169 (Gonzales et al.) describe Post CMP clean comprising TMAH.
It has been an object of at least one embodiment of the present invention to provide a process for CMP of a silicon oxynitride surface.
Another object of at least one embodiment of the present invention has been that said process should not lead to leaving a residue of silicon oxynitride particles on the surface from which the layer of silicon oxynitride was removed.
Still another object of at least one embodiment of the present invention has been that said process be readily incorporated as part of the standard process used for the formation of tungsten studs in silicon integrated circuits, particularly for the 0.18 micron logic family of circuits.
A further object of at least one embodiment of the present invention has been that said process not require additional specialized apparatus for its implementation.
These objects have been achieved by subjecting the surface from which the silicon oxynitride was removed to a high pressure rinse in an aqueous solution that includes a surfactant such as tetramethyl ammonium hydroxide or isopropyl alcohol. These surfactants serve to modify the hydrophobic behavior of the silicon oxynitride particles so that they no longer cling to the surface.